PIC to Motor Mind B

Features of a Motor Mind B

• Interfaces with a PIC using a 2-wire serial protocol. One wire transmits data to the MM from the PIC, and a second returns status information. The current version of the library only uses the send wire, so a one-wire serial interface is possible. The serial link operates at 2400 baud.
• It can drive motors up to 30V at 3.5 amps. It is packaged with a large heat sink to disipate the heat involved in driving larger motors.
• It provides speed control of motors. Speed control is achieved using Pulse Width Modulation (PWM). PWM allows you to control the speed of a motor by sending short pulses of current to it, rather than simply turning it on and off.
• Motor direction control is provided, and a motor can be reversed.
• You can drive the motors from a seperate power supply than that powering the logic side of the module. This is a very useful feature for reducing noise and brown outs on the logic power supply rails.
• If the motor has a tachometer attached, it can return the current RPM of the motor.
• In combination with the PWM feature, you can specify a speed you want the motor to remain at, and it will continually monitor the motor's speed and adjust the pulses to the motor to maintain the preset speed.

Library functions provided

• void mm_putc(char port, char pin, char c) Send the byte c to a Motor Mind B module connected to port and pin. The port parameter corresponds to the PORT location in the PIC's register file: PORTA is location 5, and PORTB is location 6. The pin parameter defines which bit of the specified port the MMB is attached to.
• void mm_start(char port, char pin, char dutycycle) Start the motor attached to port and pin. Set the dutycycle (speed) of the motor.
• void mm_stop(char port, char pin) Stop the motor attached to port and pin.
• void mm_reverse(char port, char pin) Reverse the direction of the motor attached to the specified port and pin.

Library Source Code

• motor.c C source code for the library.
• motor.lib library file.
• mmtest.jpg schematic of wiring the Motor Mind B to the PIC.
• mmtest1.c test source code to turn motor on and off only (also available as a hex file to download into the PIC).
• mmtest2.c test source code to reverse motor direction(also available as a hex file to download into the PIC).
• mmtest3.c test source code to run motor continualy, but slow it down over time (also available as a hex file to download into the PIC).

Example 1 - Turn the motor on and off

/*
 * mmtest1.c
 *
 * Motor Mind Driver library Test
 *
 * Test one: turn the motor on and off
 *
 * Motor Mind module is conected to PORTA
 * FM pin on MM is connected to  RA1 pin 18
 * LED on RB4 via 1K resistor
 *
 * Mark Crosbie 10/31/98  mark@mastincrosbie.com
 */

#define MOTOR 0x5
#define MMPIN 1
#define LED 4

void main(void) {

  set_bit(STATUS, RP0);    /* select the register bank 1 */
  clear_bit(TRISA, MMPIN);  /* Port A.1 is output to motor */
  clear_bit(TRISB, LED);   /* Port RB.4 is output LED*/
  clear_bit(STATUS, RP0);

  while(1) {

    /* start the motor at half speed */
    mm_start(MOTOR, MMPIN, 128);

    delay_s(2);

    /* stop it */
    mm_stop(MOTOR, MMPIN);

    /* flash the LED once */
    set_bit(PORTB, LED);
    delay_s(1);

    clear_bit(PORTB, LED);
    delay_s(1);
 
  }
}

Example 2 - Test reversing the motor direction

/*
 * mmtest2.c
 *
 * Test two: turn on the motor, let it run for 2 seconds, 
 * reverse direction, flash LED and then turn the 
 * motor on again
 *
 * NOTE: It is safer to stop the motor before reversing its
 * direction. If you don't then a potentially large back-EMF current
 * from the motor could destroy the PIC or the Motor Mind B module
 *
 * Motor Mind module is conected to PORTA
 * FM pin on MM is connected to  RA1 pin 18
 * LED on RB4 via 1K resistor
 *
 * Mark Crosbie 10/31/98
 */

#define MOTOR 0x5
#define MMPIN 1
#define LED 4

void main(void) {

  set_bit(STATUS, RP0);    /* select the register bank 1 */
  clear_bit(TRISA, MMPIN);  /* Port A.1 is output */
  clear_bit(TRISB, LED);   /* Port RB.4 is output */
  clear_bit(STATUS, RP0);

  while(1) {

    /* start the motor at half speed */
    mm_start(MOTOR, MMPIN, 128);

    delay_s(2);

    /* stop the motor */
    mm_stop(MOTOR, MMPIN);

    /* reverse direction */
    mm_reverse(MOTOR, MMPIN);

    /* flash LED */
    set_bit(PORTB, LED);
    delay_s(1);

    clear_bit(PORTB, LED);
    delay_s(1);
 
  }
}